97 STS overheating
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Northstar Engines and System Technical Discussion Discussion, 97 STS overheating in Cadillac Engine Technical Discussion; So I have had this overheating problem on my caddy appear after letting it sit for over a year. I ...
  1. #1
    seduxion is offline Cadillac Owners Member
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    97 STS overheating

    So I have had this overheating problem on my caddy appear after letting it sit for over a year.

    I fire it up drive down the road all is cool. Get on the hiway and WOT it to 90 and it startd dinging at me talking about overheating and coolant low.

    I pull over call the tow truck get it home.

    I started looking for leaks or signs of leaks. None. About 8 months before garaging it I replaced the water pump. I stopped driving it because I bought a jeep to drive instead (it's easier to haul the fishing gear in it).

    Anyways I drained and filled with water and cleaner. said to drive for 3 hours. Well I drive it to work 1 time a week just to get it flowing around in there. Yesterday it overheated after a brief drive to the store. It boiled out of the reservoir.

    So last night i removed the cap and thermostat. I boiled some water up to 185 and it started to open. So i know it work, but it may also be intermittently sticking. Who knows. So I will be replacing that as it's a cheap part.

    I got my buddy's snap-on cooling system tester and tested the cap. I wetted the seals and put it to the test. Pumped it to 15psi and it started letting air out. I then watched it drop to 10 psi quickly then slowly taper off at 7psi.

    I put it under a pan of water to see if the pump was leaking ot the cap. It was the cap leaking bubbles.

    I also blew compressed air through the purge line coming out of the water pump housing to clear that as well. Do not know if it was clogged or not but it can't hurt.


    I sure hope this cap is my only issue because someone I know through someone else is looking at buying the caddy for $5k and I would hate to sell it to someone I have to deal with if it's a blown headgasket. If it's the HG I am takign is straight to the dealer and trading it in before the engine warms up.

    I guess I am asking for reassurance that you all think it is the cap causing my issues here before I get too stressed over this ordeal.

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  3. #2
    ELDOminator's Avatar
    ELDOminator is offline Cadillac Owners Fanatic
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    Re: 97 STS overheating

    I'd look over the radiator hoses. Just recently I had to replace my upper hose after seeing what seemed to be a razorblade nick in it. I was lucky enough to see it bubble out a little bit when my car was overheating. All is well now, with a fresh system and tubing.

  4. #3
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 97 STS overheating

    Sure sounds like you have found the culprit, and it was cheap and easy. please follow up and let us know if that did the trick.

  5. #4
    seduxion is offline Cadillac Owners Member
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    Re: 97 STS overheating

    Well so far I have replaced the thermostat and the rad cap. I refilled with pure water not antifreeze for testing. Dexcool doesn't come cheep to spill over the ground. I sure hope this was it. Before I refilled with water I pressurized the system to 18psi. I heard a hiss coming out near the air intake. Below it I think. Really was hard to narrow down because of the road noise and the neighbor mowing the lawn. So I filled it with water and then repressurized it I saw a very small drip around the thermostat. I will need to rtv that it seems. I hope that was the air I was hearing but it doesn;t seem in the right place I heard the air whistling.

    Anyways I idled it after the first fill. and kept filling for the next 10 minutes. THe thermostat opened and I burped the air out of the upper hose. Refilled the system and then capped it. I sat in it rapped it to 3k for a bit and then up and down 5k idle 5k idle 5k idle to see if I could get it to boil over or overheat so far so good. Only a driving test will tell now I think.

    Then it's on the market.

  6. #5
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 97 STS overheating

    If all works out OK get that H2O out of there and get a 50/50 mix into it. Actually, you won't get all the water out so a 70/3 mix will be more appropriate unless you are going to use a refractometer to get it right.

  7. #6
    seduxion is offline Cadillac Owners Member
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    Re: 97 STS overheating

    Quote Originally Posted by Ranger
    If all works out OK get that H2O out of there and get a 50/50 mix into it. Actually, you won't get all the water out so a 70/3 mix will be more appropriate unless you are going to use a refractometer to get it right.
    I plan on doing a couple fill/drains to get the cleaner out of the system prior to adding antifreeze. Thanks for the heads up on the 70/30 mix!

  8. #7
    seduxion is offline Cadillac Owners Member
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    Re: 97 STS overheating

    Hrmm. Drove it to work this morning no problems. Drove it home for lunch no problems. Drove it to a client 3 miles down the road just fine. Left there after 5 minutes and came back to work about 5 miles and at a red light it started overheating. In the parking lot I see water coming out of the overflow.

    Reading above you will note I have replaced thermostat and pressure cap. However I am still running distilled water through the system. I do not see how that could cause problems. Should I bother adding Dexcool at this stage and see what it does?

  9. #8
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 97 STS overheating

    If I understand you to say that you are running straight distilled water, YES definately change to a 50/50 mix of Dex/distilled water ASAP. If for no other reason than anti corrosion protection.

  10. #9
    seduxion is offline Cadillac Owners Member
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    Re: 97 STS overheating

    before i do anything else my buddy is bringing over a combustion byproduct test kit as well as a leak down test kit tonight. I am determined to find the cause of my boiling over.

  11. #10
    seduxion is offline Cadillac Owners Member
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    Re: 97 STS overheating

    yup. the the blue turned yellow. positive for combustion leak in the coolant reservoir.

  12. #11
    sureshot is offline Cadillac Owners Member
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    Re: 97 STS overheating

    I just caught a potential overheat problem in my wife's 94.
    The water pump drive belt tensioner spring tab broke.
    The belt was moving but it was slipping badly.

    All the aftermarket parts catalogs fail to show that tensioner until you get up to 98-00.
    It's Dayco # 89317

  13. #12
    seduxion is offline Cadillac Owners Member
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    Re: 97 STS overheating

    It tested positive for a head gasket leak. I traded it in the other day for a diff vehicle.

  14. #13
    sureshot is offline Cadillac Owners Member
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    Re: 97 STS overheating

    Quote Originally Posted by sureshot
    All the aftermarket parts catalogs fail to show that tensioner until you get up to 98-00.
    It's Dayco # 89317
    Well - forget the above. That Dayco part is for the newer water pump housing that is drilled through and not just tapped.

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